Winchester disk drives include a flat, annular, rigid disk coated with a magnetic material, and a magnetic head assembly which encodes and decodes digital information in the magnetic material of the disk. The disk and head assembly are enclosed within an air-tight enclosure, and the disk is rotated rapidly around its axis by an electric motor. The head assembly moves radially across the surface of the disk between various recording tracks in the magnetic material.
The trend in the industry is to pack ever greater amounts of data onto a single rigid disk, which implies increasing the bit density on the disks. A disk's bit density is inversely proportional to the size of the magnetic domains that stores an individual bit. In other words, as the magnetic domains decrease in size, the bit density of the disk increases. To decrease the size of a magnetic domain the magnetic layer should be as thin as possible, and the distance between the head assembly and the magnetic material should be minimized.
As the separation between the head and the disk decreases, the chance of a disk head "crash" increases. In a head crash, the head assembly scrapes the surface of the magnetic layer, destroying the data stored on the disk. To minimize the chance of a head crash, the environment within the Winchester enclosure is made as free as possible of particulate matter, and the magnetic layer is made as smooth as possible.
A necessary prerequisite to a smooth magnetic surface is a smooth, polished surface on an uncoated rigid disk. While a number of materials, including plastic, have been used as base materials for a rigid disk, virtually all rigid disks in present day use are made from aluminum. Thus, the problem faced by the industry was to develop rigid disk finishing machinery capable of producing a smooth finish on an aluminum disk.
The rigid disk finishing machines of the prior art typically include a spindle which clamps to the inner circumference of a rigid disk, a motor for rotating the disk, and an abrasive member which oscillates radially back and forth across the surface of a disk. Typically, these machines process only a single disk at a time. U.S. Pat. No. 4,347,689 to Hammond discloses such an apparatus.
The disk finishers of the prior art have several noticeable disadvantages. Firstly, since the spindle is clamped to the disk the surface of the disk surrounding the inner circumference is sometimes damaged. Secondly, and again due to the clamping of the spindle to the disk, the disk cannot be polished fully from its outside circumference to its inside circumference. This, of course, reduces the useful surface area of the disk. Finally, the oscillation of the abrasive member radially across the rotating dish can produce small, overlapping spiral grooves in the surface of the disk, which can affect the ultimate performance of the disk drive unit. In a prior application, an apparatus was disclosed which is closely related to the present invention and which eliminates these problems. That apparatus, however, produced grooves which were concentric with the rigid disk when brought into contact with an abrasive strip having an oversized abrasive particle. Production of concentric grooves is detrimental in applications having a slowly moving abrasive strip or a high revolution disk.
Some rigid disk finishing machines utilize an abrasive strip which is moved across the surface of the disk. A problem with abrasive strips is that an occasional large, abrasive particle embedded in the surface of the strip can damage or ruin a disk.
An object of the present invention is to provide a surface finishing apparatus for disks and the like capable of abrasively finishing an annular surface fully and simultaneously from its inner radius to its outer circumference. Another object is to provide such an apparatus which minimizes abrasive damage to a disk or the like during the finishing operation.